It's littering, a misdemeanor punishable by a fine of no less than $200 or more than $1200. The court can also order you to pick up trash for a mile along that road. If a cop sees you throw a butt out the window, he can pull you over and cite you for it. Additionally consider that throwing a burning cigarette out the window is a fire hazard. If it starts a fire along the roadway, you may find yourself facing arson charges. Put it out IN the vehicle and stash the butts IN the vehicle until you can properly dispose of them in a trash receptor.